Thin, Planar shaped carrier with wiegand wires

ABSTRACT

A reader for a disk-shaped carrier with Wiegand wires is described which manages with only two permanent magnets (1, 2). the variation of the magnetic field needed for detecting the Wiegand wires is effected by flux concentrating pieces (3, 4, 7) attached to the permanent magnets (1, 2). In order to be able to read the carrier with the Wiegand wires without change when it is inserted into the reader rotated by 180° round its longitudinal axis coinciding with the direction of insertion (14), the flux concentrating pieces (3, 4, 7) are arranged symmetrically with respect to the longitudinal axis (14) which is a two-fold axis of symmetry. To pick-up the Wiegand pulses, two E-shaped soft magnetic cores (9) are provided which carry on their center leg an electrical sensor winding (17). The free ends of the legs of the E-shaped cores (9) face one another and are also arranged symmetrically with respect to the longitudinal axis (14).

This is a divisional of co-pending application Ser. No. 07/116,638 filedon Nov. 3, 1987 now U.S. Pat. No. 4,862,303.

The invention is based on a magnetic reader having the featuresspecified in the introductory clause of claim 1. In EP- No. 0,025,596 A1a read head is described which exhibits all features of the introductoryclause of claim 1, with the exception of the slot for the carrier withthe Wiegand wires and the guide parts which delimit the slot and guidethe carrier along a predetermined path in the slot. Such guidance isnormal and necessary in order to ensure that the Wiegand wires aresubjected to a reproducible magnetic force flux when their carrier isdisplaced in the slot.

The construction and method of functioning of Wiegand wires aredescribed in EP- No. 0,025,596 A1 and in DE-OS No. 3,340,600. Thelast-mentioned printed document also contains information concerningother bistable magnetic elements (briefly called BMEs in the text whichfollows) which have $similar characteristics to Wiegand wires.

The read head known from EP- No. 0,025,596 has an E-shaped soft magneticcore the center leg of which carries a sensor winding. The E-shaped coreis located between two permanent magnets which are arranged to beapproximately antiparallel, the arrangement being made in such a mannerthat, imagining the E to be standing up, one permanent magnet is locatedabove the top leg of the E and the other permanent magnet is locatedbelow the bottom leg of the E and the pale faces enclose an angle ofapproximately 160° with the plane spanned by the legs of the E. At somedistance from the plane spanned by the legs of the E, a third permanentmagnet is located which generates between itself and the E core amagnetic field which is directed oppositely to the magnetic fieldgenerated by the two other permanent magnets in this area.

In the known read head, the Wiegand wires are guided with their carrieralong a path of movement which extends in the immediate vicinity of theends of the three legs of the E core so that the legs are directedtowards the carrier. The known reading head operates in such a mannerthat the carrier is first moved along the third permanent magnet in thestrong field of which the Wiegand wires are magnetically saturated sothat their soft magnetic core and their hard magnetic shell exhibit thesame direction of magnetization. As it approaches the E core, eachWiegand wire passes into a magnetic field of the opposite directionwhich is generated by the two permanent magnets adjacent to the E coreand causes the soft magnetic core of the Wiegand wire to reverse itsdirection of magnetization (this process is called magnetic restorationof the Wiegand wire).

In the course of the further movement of the carrier, the Wiegand wirespass into an area in which the direction of the magnetic force flux isagain reversed (this is the field generated by the rear pole faces ofthe two permanent magnets adjacent to the E core). In this area of themagnetic field, the direction of magnetization of the soft magnetic coreof each Wiegand wire is abruptly reversed and again corresponds to thedirection of magnetization of the hard magnetic shell. In order to beable to adequately pick up the change in the magnetic force fluxoccurring when the soft magnetic core switches from the antiparalleldirection to the parallel direction of magnetization, the E-shaped coreis arranged in such a manner that the free ends of its legs are locatedas close as possible to the point at which this changeover occurs ineach case. The consequence is that the point at which the soft magneticcore of the Wiegand wires switches from the parallel direction to theantiparallel direction of magnetization is located at a slightly greaterdistance from the E-shaped core so that the change in magnetic forceflux then occurring can be less well picked up by the sensor winding onthe E core. Only the voltage pulse occurring in the sensor windingduring the switching in the direction of magnetization of the softmagnetic area from the antiparallel direction to the parallel directionof magnetization is used for evaluation.

The carrier which is moved past the E-shaped core has two rows ofWiegand wires one of which is moved past the ends of the upper and thecenter leg and the other one of which is moved past the ends of thecenter and the lower leg of the E-shaped core. The consequence is thatthe Wiegand wires of one row produce pulses of the opposite polarity inthe sensor winding to the Wiegand wires of the other row. The differentpolarity can therefore be used for determining in which of the two rowsthe respective Wiegand wire is located. This makes it possible to usethe read head to read binary coded information item which is containedin the arrangement of the Wiegand wires in two rows of the carrier ifthe significance "0" is allocated to the wires in one row and thesignificance "1" to the wires in the other row in each case.

In the known read head, the permanent magnets and the E-shaped core withthe sensor winding are all on one and the same side of the path alongwhich the carrier with the Wiegand wires is guided past the permanentmagnets and the E-shaped core. In order to be able to subject theWiegand wires to a sufficiently strong magnetic field and in order to beable to pick up as strong as possible a change in the magnetic forceflux during remagnetization of the Wiegand wires in the sensor winding,this path extends as closely as possible to the permanent magnets andthe E-shaped core and, for the same reason, the Wiegand wires areembedded into a thin multi-layer card similar to a check or credit cardof plastic, have therefore only a small distance from the surfaces ofthe card and can be moved correspondingly closely past the permanentmagnets and the E-shaped core.

In order to be able to correctly read the information contained in thearrangement of the Wiegand wires on the card-shaped carrier, the carriermust be moved along the read head in a predetermined orientation. If thecarrier is reversed so that its other surface faces the permanentmagnets and the E-shaped core, the read head reads a differentinformation item or no information at all. A further disadvantage of theknown read head consists in the fact that, due to the arrangement of athird permanent magnet in addition to the two permanent magnets arrangedon both sides of the E-shaped core, it has a relatively greatconstructional length which requires correspondingly long carriers forthe Wiegand wires because each ferromagnetic wire must be conducted pastall magnets when inserting the carrier. Neither can the distance of thethird permanent magnet from the two other permanent magnets bearbitrarily reduced because their magnetic fields would otherwise weakeneach other too much and remagnetization of the Wiegand wires would nolonger be possible.

The invention is based on the object of creating a magnetic reader whichhas as short as possible a constructional length and allows a carrierwith Wiegand wires to be inserted into the slot and read in the twopossible orientations of the large surfaces of the carrier.

This object is achieved by a reader having the features specified inclaim 1.

Advantageous further developments of the invention are the subjectmatter of the subclaims.

The result of the symmetrical arrangement of the two E-shaped cores andof the free ends of the two first flux concentrating pieces is that acarrier having two rows of Wiegand wires or wire-shaped bistablemagnetic elements of similar characteristics can be inserted rotated by180° around its longitudinal center line, which coincides with thedirection of insertion, and that the binary coded information containedon it can be correctly read out in both orientations of the carrier.Depending on the orientation of the carrier, the electric voltage pulsesare generated by magnetic induction in the sensor winding which isclosest to the Wiegand wires changing their direction of magnetization.For this purpose, the two sensor windings are preferably electricallyconnected to one another in series because only one common evaluatingcircuit is then needed for the two sensor windings.

In contrast to the known read head, the reader according to theinvention only has two permanent magnets; the third permanent magnetprovided for the magnetic saturation of the Wiegand wires in the knownread head has been omitted in the reader according to the invention inwhich the magnetic saturation, the magnetic restoration and also thetriggering of the Wiegand pulses is effected by the same two permanentmagnets. The magnetic field with high field strength, required for themagnetic saturation of the Wiegand wires, is generated at a pointlocated in front of the permanent magnets between the free ends of thefirst two flux concentrating pieces facing one another. For the magneticrestoration of the Wiegand wires, a less strong magnetic field is neededthan for their magnetic saturation. This is why a magnetic short circuitis produced by a third flux concentrating piece between the two polefaces of the permanent magnets which are not occupied by the first twoflux concentrating pieces and, as a result, the magnetic field betweenthese two pole faces is weakened, the construction and arrangement ofthe third flux concentrating piece being made in such a manner that themagnetic field weakened by the magnetic short circuit is still strongenough to effect the magnetic restoration of the Wiegand wires. Byomitting a separate permanent magnet for the magnetic saturation of theWiegand wires and by providing a magnetic short circuit between two ofthe pole faces of the remaining two permanent magnets in conjunctionwith the resultant reduced mutual influence of the magnetic field forthe saturation of the Wiegand wires, on the one hand, and of themagnetic field for their restoration, on the other hand, a much shorterconstructional length of the reader is possible than in the case of theknown read head.

The absence of a separate permanent magnet for the magnet saturation ofthe Wiegand wires results in a different type of movement of the carrierin the reader according to the invention than in the case of the knownread head: in the case of the known read head, the information locatedon the carrier is read in passing, that is to say the carrier isinserted into the end of the slot adjacent to the saturation magnet andremoved again at the opposite end of the slot. During this process, theWiegand wires first pass through the area of the magnetic saturationfield, then the area of the oppositely directed magnetic restorationfield and then again an area with a magnetic field which is directedoppositely to the restoration field and is used for triggering theWiegand pulses. In the reader according to the invention, the carriersare inserted into the slot from the end where the free ends of the firsttwo flux concentrating pieces are located between which the magneticsaturation field exists. The Wiegand wires located on the carrier thusalso first pass through the area of the magnetic saturation field andthen pass into the area of the oppositely directed magnetic restorationfield. If carried further in the original direction of movement,however, the Wiegand wires would not again pass into a magnetic fieldwhich is directed oppositely to the magnetic restoration field; this iswhy the direction of movement of the carrier is reversed after immersioninto the magnetic restoration field so that the Wiegand wires again passinto the magnetic saturation field in which the Wiegand pulses aretriggered even with a relatively low field strength. The free ends ofthe two E-shaped cores are brought towards this area where the Wiegandpulses are triggered. The reader according to the invention is thus aninsertion-type reader: the carrier with the Wiegand wires is insertedinto the slot of the reader, preferably up to a stop in order to ensurethat all Wiegand wires are inserted deeply enough into the magneticrestoration field, and then the carrier is retracted again. During theinsertion, the Wiegand wires are put into a state of magnetization fromwhich the Wiegand pulses can be triggered. During the subsequentretraction of the carrier, the Wiegand pulses are then triggered andpicked up by one or the other sensor winding.

In order to be able to insert the carrier into the reader in the twopossible orientations it is basically sufficient to arrange the two Ecores and the free ends of the first two flux concentration piecessymmetrically with respect to the longitudinal center line of the slot.Preferably, however, the entire magnetic arrangement is constructedsymmetrically with respect to this longitudinal center line of the slot,preferably also mirror-symmetrically with respect to the two mainplanes, which are perpendicular to one another, of the slot whichcontain the longitudinal center line of the slot. However, thelast-mentioned mirror-symmetrical arrangement presupposes that the tworows of the carrier in which the Wiegand wires are arranged extendmirror-symmetrically with respect to the plane containing thelongitudinal center line of the carrier and extending perpendicularlywith respect to the long side of the carrier.

Particularly in this case, it is especially advantageous to use acarrier having the features specified in claim 9; as a result of thefact that the Wiegand wires are closer to the one than to the othersurface in this carrier, it is at least achieved that Wiegand pulsesoccurring are picked up with a higher signal amplitude by the E-shapedcore closer to the Wiegand wires than by the opposite E-shaped core. Inthe case of electrically series-connected sensor windings, therefore, aresultant pulse remains from the two electric voltage pulses withopposite polarity which are produced by induction in the two sensorwindings from a triggered Wiegand wire whereas the pulses occurring inthe two sensor windings would mutually cancel if a carrier is used inwhich the Wiegand wires are arranged in the center between the surfacesof the carrier in such a manner that they influence the two E cores withapproximately, the same strength. In the area between the Wiegand wireson the one hand and the more remote surface, on the other hand, thecarrier is preferably formed of a non-magnetic metal, particularly ofelectrically highly conductive aluminum which keeps Wiegand pulses,induced by eddy current damping in the sensor winding on the E-shapedcore more remote from the ferromagnetic wires, relatively small incomparison with the pulses in the opposite sensor winding. In contrast,the Wiegand wires are suitably separated from the near-side surface onlyby one or two non-magnetic thin coverfoils, for example of a plastic orof stainless steel.

The third flux concentrating piece partially shorting the two permanentmagnets must be arranged in such a manner that the remaining weakenedmagnetic field is sufficient for magnetically restoring the Wiegandwires in both orientations of the carrier. This is best achieved byconstructing the third flux concentrating piece in such a manner that itencloses the slot into which the carrier is inserted, for example insuch a manner that the third flux concentrating piece, having aslot-shaped opening, becomes a part of the insertion slot for thecarrier. The stray magnetic field existing in this slot-shaped openingis the magnetic field for the restoration of the Wiegand wires.

Due to such a slot-shaped opening, the third flux concentrating piececan become a guide part for the carrier. The first two fluxconcentrating pieces can also be constructed in similar manner to becomeguide parts for the carrier, for example by constructing them to bebifurcated at their free ends and arranging them in such a manner thatthe narrow sides of the slot extending between them are located betweenthe legs forming the fork. This has the further advantage that themagnetic field lines do not enter the Wiegand wires axially from theends but at a greater angle with respect to the axis through the shellsurface of the Wiegand wires which is of advantage for the magneticaction of the Wiegand wires.

The attached drawing diagrammatically shows a preferred typicalembodiment of the reader according to the invention and of a carrierwith Wiegand wires which is particularly suitable for this reader.

FIG. 1 shows the arrangement of the essential components of the readerin a top view,

FIG. 2 shows the rear view of the arrangement shown in FIG. 1 (directionof viewing according to arrow II),

FIG. 3 shows the front view of the arrangement shown in FIG. 1(direction of viewing in direction of arrow III), and

FIG. 4 shows a part-sectional view of a carrier with Wiegand wires whichcan be read by means of the reader shown in FIGS. 1 to 3.

The reader contains two matching permanent magnets 1 and 2, particularlyhigh-performance magnets based on cobalt with a rare earth metal, forexample cobalt samarium magnets. These two magnets 1 and 2 are arrangedparallel to one another and at a distance from one another with matchingdirection of magnetization. The two pole faces 1b and 2a, facing awayfrom one another, of the two magnets 1 and 2 each carry a soft magneticflux concentrating piece 3 and 4 forming an L-shaped angle, the freeends 3a and 4a of which face one another, maintaining a mutual distance.The free ends of the two flux concentrating pieces 3 and 4 areconstructed to be bifurcated in mirror image matching manner, the twopairs of legs 3b and 3c and 4b and 4c jointly enclosing a slot 5 intowhich a carrier 6 with Wiegand wires can be inserted. The two pole faces1a and 2b, facing one another, of the magnets 1 and 2 are connected toone another by a third soft magnetic flux concentrating piece 7 in whichan elongated hole 8 is located which also encloses the slot 5 forinserting the carrier 6. The direction of magnetization of the twopermanent magnets is indicated by arrows 11 and 12, the direction of themagnetic force flux in the elongated hole 8 is indicated by an arrow 13and in the intermediate space between the ends 3a and 4a of the twofirst flux concentrating pieces 3 and 4 by an arrow 13.

In the area between the ends 3a and 4a of the flux concentrating pieces3 and 4, on the one hand, and the flux concentrating piece 7, on theother hand, two correspondingly constructed soft magnetic E-shaped cores9 and 10 are arranged, the three legs 9a, 9b and 9c and 10a, 10b and 10cof which face one another. The E-shaped cores are arranged at arightangle to the intended direction of movement of the carrier 6 whichis indicated by the arrow 14 in FIG. 1 and coincides with thelongitudinal center line of the slot 5, the lateral delimitation ofwhich is indicated by the two parallel lines 15 and 16 in FIGS. 1 to 3.

The two cores 9 and 10 carry on their center leg 9b and 10b,respectively, an electrical sensor winding 17 and 18, respectively. Thetwo sensor windings are electrically connected to one another in series.The two cores 9 and 10 are closer to the flux concentrating piece 7 thanto the free ends 3a and 4a of the flux concentrating pieces 3 and 4.

The carrier 6 shown in FIG. 4 consists of a flat rectangular piece ofaluminum which, for example, has a thickness of 2 mm, a width of 18 mmand a length of 75 mm. Into this piece of aluminum, a trough 21 with adepth of approximately 0.4 mm is stamped on one side into which a thinplastic strip is inserted into which two rows 22 and 23 of Wiegand wiresare embedded. The plastic strip can be, for example, two adhesive stripswhich are bonded to one another, the Wiegand wires 24 having been placedbetween them. The trough 21 is closed with a foil 25 of non-magneticstainless steel. In this manner, the Wiegand wires 24 are located veryclosely to one surface of the carrier 6, this being the surface 26covered by the stainless steel foil 25. The Wiegand wires 24 areseparated by 1.6 mm of aluminum from the opposite surface 27.

If such a carrier is inserted into the insertion reader shown in FIGS. 1to 3 with the stainless steel foil 25 pointing upwards, the Wiegandwires first pass through the strong magnetic field generated between theends 3a and 4a of the flux concentrating pieces 3 and 4 and aremagnetically saturated in this field, for which a field strength ofapproximately 80 A/m is required. As the third flux concentrating piece7 is approached, this magnetic saturation field weakens; the directionof the magnetic force flux is reversed in the area between the E-shapedcores 9 and 10 and the third flux concentrating piece 7 and in the areaof the elongated hole 8 of the flux concentrating piece 7, the Wiegandwires 24 are magnetically restored, that is to say the soft magneticcore of the Wiegand wires which has first been magnetized in parallelwith the hard magnetic shell of the Wiegand wires in the magneticsaturation field reverses its direction of magnetization and is thenmagnetized in antiparallel to the hard magnetic core. A field strengthof about 16 A/m is typically needed for this remagnetization. Thecarrier is inserted far enough for all Wiegand wires 24 to have passedthrough the elongated hole 8 in the flux concentrating piece 7. An endstop, not shown here, is suitably provided at an appropriate distancebehind the flux concentrating piece 7. After the end stop has beenreached, the carrier 6 is retracted. During the retraction movement, theWiegand wires 24 again pass into the influence of the magneticsaturation field generated between the free ends of the fluxconcentrating pieces 3 and 4. Shortly after entering the magneticsaturation field, with a low field strength of even just a few A/m, thesoft magnetic core of the Wiegand wires is abruptly remagnetized and isthen again magnetized in the same direction as the hard magnetic shell.The surge of induction occurring during this remagnetization isessentially picked up by the adjacent sensor winding 17. To obtain ahigh signal yield, the ends of the three legs 9a, 9b and 9c and 10a, 10band 10c of the E-shaped cores are directed exactly towards the point atwhich this changeover of the direction of magnetization of the softmagnetic core from its antiparallel direction to the orientationparallel to the direction of magnetization of the shell is expected(this changeover is also called the triggering of the Wiegand pulses).The Wiegand wires in the one row 22 are positioned where there are gapsin the other row 23, and vice versa. The consequence is that the Wiegandwires of row 22 generate Wiegand pulses of the opposite polarity to theWiegand wires of row 23. This makes it possible to provide a binarycoding by means of the spatial arrangement of the Wiegand wires 24 inthe two rows 22 and 23: the Wiegand wires in the one row 22 are locatedwhere there are gaps in the other row 23, and vice versa.

If the carrier 6 is reversed so that the stainless steel foil 25 and theWiegand wires 24 behind it point downwards the corresponding pulses areessentially picked up by the lower sensor winding 18. The informationread during this process is the same as in the opposite case.

We claim:
 1. A thin, generally planar-shaped carrier in which twoparallel rows of mutually parallel Wiegand wires or wire-shaped bistablemagnetic elements exhibiting similar characteristics are embedded whichextend transversely to the longitudinal direction of the rows, for usein a magnetic reader having a slot which is limited by guide parts andinto which the carrier is introduced for reading and which defines thedirection of movement of the carrier, said magnetic reader having twopermanent magnets which are arranged in the vicinity of the slot in sucha manner that the magnetic field generated by them has, behind oneanother in the direction of movement, two zones with oppositely directedfield strength vectors extending transversely to the direction ofmovement, including an inductive sensor, wherein two E-shapedferromagnetic cores extending transversely to the direction of movementare provided for forming a sensor, said cores being located on oppositelong sides of the slot and the three legs of which are directed towardsthe long side of the slot, said two cores carrying on their center legsan electrical sensor winding, a north pole face of the first permanentmagnet being connected to a first flux concentrating piece, and a southpole face of the second permanent magnent being connected to a secondflux concentrating piece, these two flux concentrating pieces beinglocated on different sides of the main plane extending perpendicularlyto the long side of the slot and containing its longitudinal center lineand their free ends facing each other, a south pole face of the firstpermanent magnet and a north pole face of the second permanent magnetbeing connected to one another by a third flux concentrating piece, theE-shaped cores being arranged between free ends of the first two fluxconcentrating pieces on one hand and the third flux concentrating pieceon the other hand, and the cores and the free ends of the first two fluxconcentrating pieces being arranged symmetrically with respect to thelongitudinal center line of the slot which is an axis of symmetry havingtwo-fold symmetry, wherein said carrier has two large surfaces, andWiegand wires are located closer to one than to the other one of the twolarge surfaces.
 2. Carrier as claimed in claim 1, which consists of anon-magnetic metal, particularly of aluminum, in the area between theWiegand wires and one of the large surfaces of the carrier which surfaceis more remote from these wires.
 3. Carrier as claimed in claim 2, whichhas a thickness of between 1.5 mm and 3 mm, in particular 2 mm, and hason one side a tub-shaped recess which as a depth of between 0.3 and 0.5mm and in which the Wiegand wires are arranged.
 4. Carrier as claimed inclaim 1, wherein the Wiegand wires are only separated from the nearsurface of the carrier by one of two thin non-magnetic cover foils. 5.Carrier as claimed in claim 4, which has a thickness of between 1.5 mmand 3 mm, in particular 2 mm, and has on one side a tub-shaped recesswhich has a depth of between 0.3 and 0.5 mm and in which the Wiegandwires are arranged.
 6. A thin, generally planar-shaped carrier in whichtwo parallel rows of mutually parallel Wiegand wires or wire-shapedbistable magnetic elements exhibiting similar characteristics areembedded which extend transversely to the longitudinal direction of therows, for use in a magnetic reader having a slot which is limited byguide parts and into which the carrier is introduced for reading andwhich defines the direction of movement of the carrier, said magneticreader having two permanent magnets which are arranged in the vicinityof the slot in such a manner that the magnetic field generated by themhas, behind one another in the direction of movement, two zones withoppositely directed field strength, vectors extending transversely tothe direction of movement, including an inductive sensor, wherein twoE-shaped ferromagnetic cores extending transversely to the direction ofmovement are provided for forming a sensor, said cores being located onopposite long sides of the slot and the three legs of which are directedtowards the long side of the slot, said two cores carrying on theircenter legs an electrical sensor winding, a north pole face of the firstpermanent magnet being connected to a first flux concentrating piece,and a south pole face of the second permanent magnet being connected toa second flux concentrating piece, these two flux concentrating piecesbeing located on different sides of the main plane extendingperpendicularly to the long side of the slot and containing itslongitudinal center line and their free ends facing each other, a southpole face of the first permanent magnet and a north pole face of thesecond permanent magnet being connected to one another by a third fluxconcentrating piece, the E-shaped cores being arranged between free endsof the first two flux concentrating pieces on one hand the third fluxconcentrating piece on the other hand, and the cores and the free endsof the first two flux concentrating pieces being arranged symmetricallywith respect to the longitudinal center line of the slot which is anaxis of symmetry having two-fold symmetry, wherein said carrier has twolarge surfaces, and Wiegand wires are located closer to one than to theother one of the two large surfaces, wherein a non-magnetic metal,particularly of aluminum, is disposed in the area between the Wiegandwires and one of the large surfaces of the carrier, which surface ismore remote from these wires.
 7. A thin, generally planar-shaped carrierin which two parallel rows of mutually parallel Wiegand wires orwire-shaped bistable magnetic elements exhibiting similarcharacteristics are embedded which extend transversely to thelongitudinal direction of the rows, for use in a magnetic reader havinga slot which is limited by guide parts and into which the carrier isintroduced for reading and which defines the direction of movement ofthe carrier, said magnetic reader having two permanent magnets which arearranged in the vicinity of the slot in such a manner that the magneticfield generated by them has, behind one another in the direction ofmovement, two zones with oppositely directed field strength vectorsextending transversely to the direction of movement, including aninductive sensor, wherein two E-shaped ferromagnetic cores extendingtransversely to the direction of movement are provided for forming asensor, said cores being located on opposite long sides of the slot andthe three legs of which are directed towards the long side of the slot,said two cores carrying on their center legs an electrical sensorwinding, a north pole face of the first permanent magnet being connectedto a first flux concentrating piece, and a south pole face of the secondpermanent magnet being connected to a second flux concentrating piece,these two flux concentrating pieces being located on different sides ofthe main plane extending perpendicularly to the long side of the slotand containing its longitudinal center line and their free ends facingeach other, a south pole face of the first permanent magnet and a northpole face of the second permanent magnet being connected to one anotherby a third flux concentrating piece, the E-shaped cores being arrangedbetween free ends of the first two flux concentrating pieces on one handand the third flux concentrating piece on the other hand, and the coresand the free ends of the first two flux concentrating pieces beingarranged symmetrically with respect to the longitudinal center line ofthe slot which is an axis of symmetry having two-fold symmetry, whereinsaid carrier has two large surfaces, and Wiegand wires are locatedcloser to one than to the other one of the two large surfaces, whereinthe Wiegand wires are only separated from the near surface of thecarrier by one or two thin non-magnetic cover foils.
 8. A thin,generally planar-shaped carrier for use in a reader having a read headprovided with permanent magnets and two oppositely arranged E-shapedcores, each provided with a sensor winding and defining a slottherebetween for the insertion of said carrier, comprising two parallelrows of mutually parallel Wiegand wires or wire-shaped bistable magneticelements exhibiting similar characteristics embedded in a carrier bodyand which extend transversely with respect to the longitudinal directionof the rows, said Wiegand wires being located closer to one than to theother one of two large surfaces of the carrier body.